In the field of thermal printing and the use of heat-sensitive, coated paper or like record material in the printing operation, the presence of the dye solution in the coating formulation or the formulation of the substrate itself has resulted in certain precoloring conditions which affect the quality of print and usefulness of the paper. As is well-known in the impact printing art, the carbonless paper, useful for transferring ink material to one or more additional sheets, is generally coated with microscopic capsules containing at least one of the reactive ingredients which produce the mark that is initiated by an impact element against the paper and which impact element causes eruption of the capsules and release of the ink material dye.
In a typical and well-known arrangement, a top or first sheet of a manifold of sheets may include a coating on the back surface thereof and such sheet is referred to as a "CB" sheet, one or more intermediate sheets may include a coating on the front surface and a coating on the back surface and which are termed "CFB" sheets, and the bottom or last sheet has a coating on the front surface and is referred to as a "CF" sheet. The direct impact on the top or CB sheet causes a mark thereon to be transferred by rupturing the capsules on the back thereof, the CFB sheet causes formation of the mark by reaction with the coating on the front and transfer of such mark through rupture of the capsules on the back of the intermediate sheet, and the CF sheet is marked by reaction with the coating on the front thereof in a manner to provide the mark on all sheets.
It has been found that during handling of a stack of CFB sheets or a roll of CFB paper having the capsular formulation, a front coating of one sheet or layer of the roll may be in contact with a back coating of an adjacent sheet or layer and such handling or perhaps rough treatment of the stack or roll of paper may cause inadvertent rupture of the capsules in the back coating, allow the dye to transfer to the adjacent sheet or layer or to mix with other reactants, and thereby precolor the paper. Additionally, a CFB sheet having a CF coating on the front surface and a CB capsular coating on the back surface may be subject to precoloring due to inadvertent contact of the reactant particles or coating material.
Representative documentation in the field of carbonless paper relative to the present invention includes U.S. Pat. No. 3,421,894, issued to H. H. Baum on Jan. 14, 1969, which discloses a paper-like sheet having a layer of heat-meltable wax with chromogenic material particles disposed therein. The layer of wax is heated to its melting point, subjected to ultraviolet light to form an image, and then reheated to a temperature where the image turns blue to fix the image.
U.S. Pat. No. 3,445,261, issued to S. G. Talvalkar on May 20, 1969, discloses heat-sensitive record material comprising a paper base sheet, a coating of acidic particles and colorless chromogenic particles, and a protective film of polyvinyl alcohol having dispersed therein to the extent of about 2% fine particles of a lubricating or powdered nontacky wax in the coating.
U.S. Pat. No. 3,674,535, issued to J. H. Blose et al. on July 4, 1972, discloses heatsensitive record material comprising a paper base sheet and a coating of colorless chromogenic material and a bisphenol distributed in a polyvinyl alcohol in combination with a filler such as clay, a lubricant such as zinc stearate and a powdered nontacky wax.
U.S. Pat. No. 4,062,567, issued to N. Macaulay on Dec. 13, 1977, discloses dual system carbonless paper in a manifolded set comprising at least two different types or systems of intermediate sheets, one sheet of which has a front coating capable of reacting with the back coating of the other sheet to produce a color. The manifolded set has one CFB sheet with front and back coatings wherein the reactive material in the back coating of each intermediate sheet is incapable of reacting with the material in the front coating of the same sheet and such CFB sheets may be stacked without danger of inadvertent coloration during handling and storage.
U.S. Pat. No. 4,197,346, issued to M. F. Stevens on Apr. 8, 1980, discloses a self-contained pressure-sensitive record material having a substrate and a coating of a mixture of pressure-rupturable capsules of an oily solvent solution of colorless chromogenic material and capsules of solid acidic resin particles. The acidic resin reacts with the chromogenic material to produce a color and has less print bleed than known self-contained systems.
U.S. Pat. No. 4,321,093, issued to M. E. Seitz on Mar. 23, 1982, discloses a color developer ink for use in producing a CF coating applied by a printing press and wherein an oil or wax may be added as a replacement for a portion of the solvent to alleviate the printing problem with loose paper fibers.
And, U.S. Pat. No. 4,343,494, issued to G. H. Ehrhardt et al. on Aug. 10, 1982, discloses a pressure sensitive, carbonless copy, paper system having a wax base hot-melt type coating for one surface containing a zinc chloride or like metallic salt and acidic halogen neutralizing agent solution, and an image receptor coating for the other surface employing phenyl methenol as a dye precursor-type chromogenic reagent material.